119 



potato-farina, Indian meal, rice, rye, barley, oats, or pea and bean meal, 

 and occasionally bone dust. The former of these are readily detected 

 by chemical means, the latter almost entirely by the aid of the micro- 

 scope. 



The microscopic characters of wheat flour are clear and distinct, 

 resting upon the shape, size, and markings of the starch grains. These 

 are large and small bodies composing the chief bulk of the flour ; the 

 smaller grains are globular in form, and do not present any very strik- 

 ing characters ; the large ones, howevei", consist of flattened round disks, 

 convex on one side, flattened on the other ; in the centre is a minute 

 spot, around which is a series of concentric rings extending to the mar- 

 gin. This spot is more or less visible in all starch grains, though it is 

 very variously shaped and placed, and the annular markings, which in 

 wheat starch form very delicate and scarcely preceptible rings, pre- 

 sent a very vai-ied, yet, in each respective kind of grain, persistent 

 appearance. These characters are modified by circumstances ; disease 

 or decay will entirely change their appearance, if not obliterate them 

 altogether. Moisture and heat rupture the grain, and hence we may 

 readily determine whether samples of flour have been ground from 

 sound, diseased, or damaged corn, by the more or less distorted appear- 

 ance of the starch grains. The microscopical characters of the other 

 starches with which wheat may be contaminated are equally distinct. 

 [Magnified drawings of these and the other articles were exhibited.] 



Besides a mici'oscopical examination, the samples of flour were 

 submitted to careful chemical analysis. One thousand grains of flour 

 worked into a dough with water, were kneaded in a fine hair sieve, 

 under a stream of cold water; we thus obtained a milky fluid passing 

 through the sieve, and a glutinous mass remaining in it. 



The milky liquid deposits starch, from which the clear supernatant 

 liquid is decanted and boiled ; a coagulum of albumen separates, which 

 is washed, dried, and weighed ; the clear liquid, separated, is evaporated 

 to dryness in a water bath, and yields sugar and gum. 



The glutinous mass left in the sieve is boiled, first in strong and then 

 in weak alcohol ; the solutions mixed and filtered while hot, give a resi- 

 due of fibrlne, while the hot alcoholic solution deposits cascine on 

 cooling; the filtered solution being evaporated to a syrup, and water 

 added, a precipitate of pure gluten is formed. Thus, by carefully 

 collecting and drying the various deposits we can weigh them, and 

 determine with great accuracy the proportions of bran or fibrin, 

 cascine, gluten, starch, albumen, sugar, and salts ; the amount of water 

 being determined in the usual way, by loss at a temperature of 212". 

 Such a complete analysis as this is not, however, necessary or desirable 



